The present invention relates to engine timing apparatus for measuring the advance/retard time delay of a multi-cylinder internal combustion engine.
It is conventional practice in the tuning of internal combustion engines to measure the advance or retard angle of the engine and adjust the angle to predetermined specifications. In this regard, a visible timing mark is provided on the engine flywheel, and a stroboscopic lamp or "timing light" is directed at the flywheel to illuminate the the timing mark. The timing light is energized under the control of ignition pulses from the ignition system, so that timing mark appears to be stationary when illuminated by the timing light. By adjusting the time delay between the ignition pulse and the firing of the timing light, the timing mark on the flywheel can be made to appear to align with a fixed mark on the engine block which corresponds to a predetermined position of the engine, typically the top dead center position of the piston in the cylinder from which the ignition pulses are being derived. The amount of time delay adjustment is indicative of the advance or retard angle of the engine.
In a gasoline engine, ignition is caused by a spark, and typically occurs before the piston reaches the top dead center position. Thus, the angle between the position of the flywheel at the point of ignition and at the top dead center position is referred to as an "advance" angle. In diesel engines, the ignition results upon injection of fuel into a cylinder heated by compression, and typically occurs a short time after the top dead center position. Thus, the angle between the position of the flywheel at ignition and top dead center is referred to as a "retard" angle.
In prior engine timing apparatus, it is common to have a metered timing light with an adjustment knob. In such an apparatus, the user adjusts the delay of the flash until the timing marks on the engine are aligned and then reads the advance or retard angle from the meter. If the angle is not according to specifications, the necessary adjustments on the engine are made. But the time delay will vary with engine speed and, therefore, at a different engine speed the meter will read a different advance/retard angle.
It is known to provide timing lights which are meterless, but which have adjustment dials which are calibrated in degrees of advance or retard angle. In such systems, the operator dials the desired advance/retard angle and the system generates the necessary delay, which automatically varies in response to changes in engine speed. One such system is disclosed in U.S. Pat. No. 4,095,170. However, that system is an analog system and, therefore, does not permit very accurate adjustment of the advance/retard angle. Furthermore, it is capable of generating only advance delays and, therefore, cannot readily be used with diesel engines.
Another such system is disclosed in U.S. Pat. No. 4,472,779, which is a digital system and can register advance and retard angles. However, the device of this patent is a large, complicated engine analyzer disposed in a floor-mounted cabinet. It is very expensive and not portable. Furthermore, this system requires, in addition to a connection to the test cylinder, a connection to the high tension lead, i.e., the coil tower wire, which may not be directly accessible in many engines. Also, the system requires the operator to know how many cylinders are in the engine and to enter that information into the system. Finally, this system is not readily adaptable for use on diesel engines since, while it is capable of registering retard angles, it may not be able to register them over a full range of from 0.degree. to -180.degree.. This is because the system operates in such a way that the retard angle is limited to the number of degrees between adjacent cylinders.
Finally, all of the prior systems suffer from inaccuracies resulting from inherent system delays. Thus, all of these systems require a finite time to respond to the ignition signal, this delay varying with the hardware and/or software being used. Even microprocessor-based digital systems may require anywhere from 50 to several hundred microseconds to respond. This error may not be significant when the engine is operating at relatively low speeds, but may be very significant at high speeds. For example, if the engine is operating at 9,000 rpm, the advance or retard angle may represent a delay of only 100 or 200 microseconds. At this speed, an error of only 50 to 100 microseconds would be very significant.